1. Field of the Invention
This invention relates to Group IIIA element fluoride-containing coatings for use in improving the corrosion resistance of members to be exposed to a corrosive halogen species-containing atmosphere, and coated members having such coatings.
2. Background Art
The applications where corrosive halogen species are present include plasma-assisted processes (e.g., plasma etching and plasma CVD) for semiconductor manufacture, incinerators and the like. In the semiconductor process, objects are etched, cleaned or otherwise treated utilizing the activity of corrosive halogen species. At the same time, members used in the atmosphere where such active halogen species are present are also affected thereby, undergoing corrosion. To minimize such impacts, highly corrosion resistant materials are under study. The members used in the corrosive atmosphere include ceramic materials such as sintered alumina, sintered magnesia, sintered aluminum nitride, and sintered yttrium aluminum double oxide, graphite, quartz, silicon, metal materials such as aluminum alloys, anodized aluminum alloys, stainless alloys, and nickel alloys, and non-metallic materials such as polyimide resins.
Metal base materials are often used at sites where electroconductivity is necessary and as housings because large size members thereof can be easily worked. Quartz, silicon and graphite members cause less contamination to the silicon semiconductor process because of high purity and are thus used in wafer surroundings within the processing container. Ceramic materials have electric insulation and relatively high durability to corrosive halide gases as compared with other materials and are thus used at sites where electric insulation or durability to corrosive halide gases is necessary.
It has also been studied to react ceramic materials such as alumina, magnesia, aluminum nitride, and yttrium aluminate with elemental fluorine to convert only the surface to a fluoride.
JP-A 2002-252209 discloses a method for further improving the corrosion resistance of a member by forming a thermally sprayed coating or sintered layer of yttrium fluoride instead of yttrium oxide on the member for thereby preventing the chemical change from yttrium oxide to yttrium fluoride.
Reference is made to Japanese Patent No. 3,017,528, Japanese Patent No. 3,243,740 (U.S. Pat. No. 5,798,016), Japanese Patent No. 3,261,044, JP-A 2001-164354, JP-A 2002-252209, JP-A 2002-222803, JP-A 2001-97791, JP-A 2002-293630 and Thermochimica ACTA, 87, 1985, 145.
Under the recent trend of semiconductor circuits being miniaturized, it becomes necessary to manage dusting from members and contamination by members to a higher extent. There is a demand for further enhancement of corrosion resistance. To meet such requirements, attempts have been made to construct members from high corrosion resistance materials as compared with conventional materials such as Y2O3, yttrium aluminate and MgF2, or to form coats of these corrosion resistant materials on exposed surfaces of ceramic and metal substrates by deposition techniques like thermal spraying, CVD and PVD, as mentioned above. There is a need for coatings having higher corrosion resistance.